Hi guys, I've recently got my Canon R7 with an 18-50 F2.8 lens. However, as a planespotter/carspotter, I'm looking for a good and cheap planespotting lens to use. After spending lots of time searching, I've narrowed it down to the following: Canon EF 70-200mm F4L (IS Version) and the RF 100-400mm F5.6-8. I'll write down here what I believe are the advantages of these lenses. (both are around the same price of \~$800)  
  
**Canon EF 70-200mm F4L IS USM:** On the disadvantages side, it's second-hand, and using EF requires an adapter, which might cause more issues with the autofocus, and I'm not really sure if 200mm (330mm equiv.) would be enough for planespotting. On the advantages side, it has a really fast aperture for that price range, along with things like internal zooming, distance scale, weather sealing, and supposedly really good sharpness throughout the zoom range. accompanied by a wider focal length, as my short lens only goes up to 50mm.  
  
**Canon RF 100-400mm F5.6-8 IS USM:** On the bad side, it has a really slow aperture going up to F8 at maximum focal length, and although I don't really shoot in low light (but I do indoors), I'm not sure how much this will affect me as I'm planning to use the long lens for sports and planespotting. However, at that same price range, I could get this lens brand new with a warranty (manufacturer's defects only, though), and since it is from the native RF mount, its autofocus will be tenfold faster (supposedly), and there is an extra 300mm reach (APSC equivalent), which might be useful for planespotting? I'm not sure tho...  
  
If you have any experience using these lenses, please share with me as much as you know, as I'm planning on getting a lens this/next weekend, or if you have any other better lenses to recommend around the price range of $700, including an adapter if needed, it would be much appreciated if you could let me know too :>

Canon EF 70-200mm F4 or RF 100-400mm F5.6-8 (For Canon R7)